R. Milne et al., Spruce budworm elastase precipitates Bacillus thuringiensis delta-endotoxin by specifically recognizing the C-terminal region, INSEC BIO M, 28(12), 1998, pp. 1013-1023
A gut juice protein from Choristoneura fumiferana (spruce budworm) larvae t
hat precipitates certain delta-endotoxins shows a unique specificity for th
e C-terminal amino acid sequence. Using homolog scanning mutants, we have i
dentified a contiguous region of the Cry1Aa toxin which interacts with the
75-kDa toxin precipitating protein (TPP-75)(1) resulting in precipitation.
The contiguous region from Cry1Aa can be transferred to Cry1Ac and results
in an identical precipitation reaction. The precipitation reaction occurs r
apidly and is unique in that the ratio of precipitating protein to toxin is
low (estimated at 0.01), unlike antibody-antigen reactions which exhibit m
ole ratios close to 1. TPP-75 has been characterized as an elastase-like se
rine protease. We have taken advantage of this serine protease character an
d incorporated a radiolabel using an irreversible inhibitor. The radiolabel
has allowed us to show the coincidence of the catalytically-inhibited TPP-
75 with the toxin in a blotting assay and to follow the degradation of TPP-
75 during storage. TPP-75 represents the first evidence that gut juice prot
eins may selectively attenuate the activity of delta-endotoxins, prior to b
inding to putative receptors on susceptible cells. TPP-75 should be evaluat
ed as a possible resistance mechanism for those larvae that do not exhibit
a receptor-based resistance. (C) 1998 Elsevier Science Ltd. All rights rese
rved.